This invention relates to vehicle occupant restraint systems and more particularly to automatically inflatable, seamless bags for use with impact-actuated vehicle occupant restraint systems.
Impact-actuated inflatable occupant restraint systems typically comprise a source of non-combustible inflating gas and a folded inflatable air bag. Detectors sense deceleration of the vehicle due to impact and actuate a source of inflating gas. The gases inflate the folded air bag to provide a resilient restraint for absorbing the kinetic energy of the occupant's body.
Most previous inflatable air bags have been constructed from multiple sheets of fabric stock which are seamed together. Typically two flat sheets of flexible material are arranged to form a top sheet and a bottom sheet. The sheets are joined at a seam along their respective edges to form a closed compartment. An opening to communicate with the gas source is formed either in the seam or in one of the sheets. Alternatively, the prior art teaches that a patterned single flat sheet may be first folded so that its edges overlie one another and then joined at these edges. In either approach, a seam has been created.
Several disadvantages result from constructing an air bag using such seams. All seams, whether sewn, dielectric, sonic or adhesive in nature, present a potential point of failure of the bag. A seam does not provide the continuity of strength, stretchability and flexibility of a continuous sheet of material. A seam also presents opportunity for air leakage which adversely affects the designed control of air flow. A sewn seam can fail due to a dropped stitch, weak thread, improper alignment of material or stitches, thread deterioration, a broken needle or material weakened due to manufacturing techniques. Any seam may fail during use due to the pressures and heat associated with gas generation and rapid inflation. Seams must be inspected for these potential problems. This testing or inspection can also weaken the seam. Finally, many of these potential problems of a seam are unobvious and an inspection may overlook the potential failure point.
An alternative prior art construction utilizes molded air bags or air bags made of formable material. However, such air bags are costly to manufacture and inspect, and they may fail due to undetectable weaknesses.
The present invention provides a reliable and inexpensive inflatable air bag for use with vehicle occupant restraint systems Broadly, the inflatable air bag of the present invention is constructed of a single piece of flat, flexible sheet material, which may be circular or of another shape. The sheet is substantially larger, in all cross-dimensions than the outlet or nozzle of the inflating gas generator with which the bag is associated. The free edge of the sheet is gathered and attached about the outlet of the gas inflator and forms a seal between the bag and the outlet, thereby forming a series of radial pleats in the sheet material. One preferred manner of attachment, which will be disclosed in detail in the following description of the preferred embodiment of the invention, utilizes a number of apertures spaced about the free edge of the sheet and fixed over a smaller number of studs or posts extending parallel to one another at regular intervals around a retaining ring. Each stud extends through a number of apertures in the sheet thereby gathering the edge so as to form radial pleats. By way of example, the bag may have 60 holes formed about its perimeter and these holes may be arranged over 20 studs formed on the ring with three adjacent holes gathered over each stud. The radial pleats thereby formed have a maximum width at the free edge, and decrease in width as they extend outwardly toward the center of the sheet. The studs of the retaining ring engage additional support structures to secure the sheet material about the outlet of the gas-generating apparatus in a relatively gas impervious manner. Various other approaches for gathering the material around the gas outlet are described herein.
To control the inflated bag to assume a relatively elliptical shape, elongated tethers may be provided with one end secured to the interior surface of the sheet material. The other end of a tether is then anchored to a stud on said retaining ring to control the shape of the bag on inflation. The bag is thus restrained from achieving a spherical shape during inflation.
Additionally, exhaust holes within the bag may be utilized. The exhaust hole or holes provide a release for excess inflation gas and allow for deflation of the air bag after use.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the appended claims, taken in conjunction with the accompanying drawings.